Patent Application
20100085547
The present invention relates to an extreme ultraviolet (EUV) radiation source, and a lithographic apparatus that includes such a source.
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
In order to be able to project ever smaller structures onto substrates, it has been proposed to use EUV radiation which is electromagnetic radiation having a wavelength within the range of 10-20 nm, for example within the range of 13-14 nm. It has further been proposed that EUV radiation with a wavelength of less than 10 nm could be used, for example within the range of 5-10 nm such as 6.7 nm or 6.8 nm.
Radiation may be produced using plasma. The plasma may be created, for example, by directing a laser at a fuel, such as particles of a suitable material (e.g. tin), or a stream of a suitable gas or vapor, such as Xe gas or Li vapor. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector such as a mirrored normal incidence radiation collector, which receives the radiation and focuses the radiation into a beam. Such a radiation source is typically termed a laser produced plasma (LPP) source.
In addition to radiation, the plasma of a plasma radiation source produces contamination in the form of particles, such as thermalized atoms, ions, nanoclusters, and/or microparticles. The contamination is output, together with the desired radiation, from the radiation source towards the radiation collector and may cause damage to the normal incidence radiation collector and/or other parts. For example, LPP sources that use tin (Sn) droplets to produce the desired EUV may generate a large amount of tin debris in the form of: atoms, ions, nanoclusters, and/or microparticles. Herebelow, reference is made to the term particulate, which means to encompass any debris or contamination in the form of atoms/ions or atom clusters from the fuel source. It is desirable to prevent the debris from reaching the radiation collector, where it may reduce EUV power, or end somewhere in the source vessel where it may create other problems. To stop especially the ions, a buffer gas can be used, but with this kind of debris mitigation, a large flow of buffer gas may be needed, which may make it desirable to have large pumps and a large supply of buffer gas. Due to the large flow of the buffer gas, the plasma region may become instable, but the flow may not stop micro-droplets of fuel from being deposited on the walls of the source vacuum chamber.
In addition, EUV LPP sources generate a large amount of fuel debris of which a part may be deposited in the central cone. The present invention is concerned with preventing build up of fuel debris deposits in the inner cone, of which uncontrolled release may damage the optics arranged in the plasma source.
It is desirable to remove fuel debris before the debris reaches the radiation collector. It is also desirable to avoid accumulation of any fuel debris onto surfaces within a radiation source.
According to an aspect of the invention, there is provided a source module for a lithographic apparatus. The source module includes a chamber defined by chamber walls, an extreme ultraviolet radiation generator that includes a fuel supply configured to supply a fuel to a plasma formation site within the chamber, a reflective element in the chamber configured to reflect extreme ultraviolet radiation emanating from a radiation emission point at the plasma formation site; and a fuel particulate interceptor, arranged in the chamber adjacent to one or more of the chamber walls, and comprising a material having an affinity for the fuel. A laser may be configured to emit a beam of radiation to the plasma formation site so that a plasma that emits extreme ultraviolet radiation is generated when the beam of radiation impacts the fuel. The fuel particulate interceptor is configured to collect fuel particulates emitted by the plasma. The fuel particulate interceptor is arranged in the chamber and comprises a material having an affinity for the fuel so that when the fuel particulates impact a surface of the fuel particulate interceptor, the fuel particulates will adhere to the surface. The fuel particulate interceptor is arranged relative to the reflective element so as to prevent any fuel particulates from falling under the influence of gravity onto the reflective element.
According to an aspect of the invention, there is provided a lithographic apparatus that includes the above-described source module and a projection system constructed and arranged to project the patterned radiation onto a substrate.
According to an aspect of the invention, there is provided a radiation source configured to generate extreme ultraviolet radiation. The radiation source includes a fuel supply configured to supply a fuel to a plasma formation site, a laser configured to emit a beam of radiation to the plasma formation site so that a plasma that emits extreme ultraviolet radiation is generated when the beam of radiation impacts the fuel, and a fuel particulate interceptor constructed and arranged to shield at least part of the radiation source from fuel particulates that are emitted by the plasma. The fuel particulate interceptor includes a first portion and a second portion, the second portion being positioned closer to the plasma formation site than the first portion, and the first portion being rotatable. The radiation source also includes a fuel particulate remover constructed and arranged to remove fuel particulates from a surface of the fuel particulate interceptor and to direct the fuel particulates towards a collection location.
According to an aspect of the invention, there is provided a lithographic apparatus that includes the above-described radiation source, and a projection system constructed and arranged to project the patterned radiation onto a substrate.
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:
The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.
The support structure MT holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure MT may be a frame or a table, for example, which may be fixed or movable as required. The support structure MT may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general teen “patterning device.”
The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.
The patterning device may be reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix.
The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”.
As here depicted, the apparatus is of a reflective type (e.g. employing a reflective mask).
The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more patterning device tables). In such “multiple stage” machines, the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.
Referring to
The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the support structure MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.
The depicted apparatus could be used in at least one of the following modes:
1. In step mode, the support structure MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.
2. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion.
3. In another mode, the support structure MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.
Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.
The radiation may be focused in a virtual source point 12 (i.e. an intermediate focus IF) disposed at or near an aperture in the chamber 7. From chamber 7, the radiation beam 16 is reflected in illumination system IL. A patterned beam 17 is formed which is imaged by projection system PS via reflective elements 18,19 onto wafer stage or substrate table WT. More elements than shown may generally be present in the illumination system IL and the projection system PS.
One of the reflective elements 19 may have in front of it a numerical aperture (NA) disc having an aperture therethrough. The size of the aperture determines an angle subtended by the patterned radiation beam 17 as it strikes the substrate table WT.
In other embodiments, the radiation collector is one or more of a radiation collector configured to focus collected radiation into the intermediate focus IF; a radiation collector having a first focal point that coincides with the source and a second focal point that coincides with afore mentioned intermediate focus IF; a normal incidence radiation collector; a radiation collector having a single substantially ellipsoid radiation collecting surface section; and a Schwarzschild radiation collector having two radiation collecting surfaces.
Also, in another embodiment, the EUV radiation generator may be a laser produced plasma (LPP) source including a light source, such as for example a CO2 laser, that is configured to focus a beam of coherent light, of a predetermined wavelength, onto a fuel such that a plasma is produced that emits at least EUV radiation. In an embodiment, the radiation source may be a discharge produced plasma (DPP) source.
In case the source SO of the embodiment shown in
The emanating EUV beam 32 may be intercepted by a suitable debris mitigation system, such as contamination trap 34, configured to collect or to deflect particle debris emanating from the region 26. The EUV beam 32A substantially free of debris may then enter a subsequent optical system 36 of the radiation source or of the lithographic apparatus, such as illumination system IL of the lithographic apparatus configured to suitably condition the beam 32A. The radiation source module 3 may include a buffer gas for cooperating with a source of laser produced plasma. Desirably the buffer gas has high transmission for in-band EUV and absorbs secondary radiation. The buffer gas may have at least 50% transmission for the EUV radiation, and at least 70% absorption for the secondary radiation. Desirably, the buffer gas has at least 90% or at least 95% transmission for the EUV radiation. It is further desirable that the buffer gas has at least 90% absorption for the secondary radiation. In the embodiments illustrated in
Typically, only a portion of the whole droplet of tin will contribute to EUV radiation generation and part of the droplet will be converted into debris. The debris may reduce the reflectivity of the radiation collector mirror, which may result in a decrease in productivity of the lithographic apparatus. The buffer gas may be provided to stop the tin debris (e.g., ions, particles, neutrals and vapor) from reaching the radiation collector 10. In instances where tin reaches the radiation collector 10, the tin may not be removed and/or when removed, the tin may deposit on unwanted surface. Without being bound to theory, plasma formation and fuel particulate formation in the plasma formation site may result in a dominant direction of fuel particulates resultant from the plasma formation site 26 (see
During operation of the radiation source, the fuel particulate interceptor 50 is operative to intercept fuel particulate, debris and vapor 40, that is formed from the plasma formation site 26 which comprises aforementioned plasma P and ejected into the chamber 7. To that end, a temperature controller (not shown in
At the temperature of 450° C., particulate debris that reaches the fuel particulate interceptor surface is melted or kept in liquid phase, so that a liquid layer is formed on the fuel particulate interceptor surface. The gravitation field (represented by the arrow g) may force the fuel in the layer to move towards a liquid fuel removal line or outlet 52 and surface tension forces should keep the liquid layer attached to the fuel particulate interceptor 50. In this way, the fuel debris may be removed from the fuel particulate interceptor 50 and subsequently from the chamber 7 of the radiation source. Although the outlet 52 may be shaped in a channel form, the orientation of the cylindrical interceptor 50 may in itself define a direction of flow, without further specific design for an outlet 52.
As illustrated in
As indicated in
Embodiments illustrated in
In some aspects, although the disclosed embodiments discuss placement of the fuel particulate interceptor placed ‘above’ a reflective element, in another aspect, the fuel particulate interceptor may be arranged in a dominant direction of the particulate formation. In particular, in such embodiments, a fuel particulate interceptor may be arranged to shield at least part of the chamber from fuel particulates emitted by the plasma, to prevent formation on the wall of a dominant contamination region.
In some aspects, the invention may be characterized by a radiation source configured to generate extreme ultraviolet radiation, the radiation source comprising: a chamber; a fuel supply configured to supply a fuel to a plasma formation site within the chamber; a laser configured to emit a beam of radiation to the plasma formation site so that a plasma that emits extreme ultraviolet radiation is generated when the beam of radiation impacts the fuel; a fuel particulate interceptor configured to shield at least part of the chamber from fuel particulates emitted by the plasma; a heater configured to heat the fuel particulate interceptor to a temperature greater than the melting temperature of the fuel; and a fuel outlet constructed and arranged to allow excess fuel and at least some of the fuel particulates to exit the chamber.
The heater may be formed by the plasma formation so that no additional heater is needed. In addition, fuel particulates adhered to the interceptor 50 may be removed by other removing means, such as chemical removal.
Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.
The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.
While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.
This application claims the benefit of priority from U.S. Provisional Patent Application Ser. Nos. 61/136,686, filed on Sep. 25, 2008, and 61/193,704, filed on Dec. 17, 2008, the entire contents of both applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61136686 | Sep 2008 | US | |
| 61193704 | Dec 2008 | US |
